Summary
A trait coordination network is constructed through intercorrelations of functional traits, which reflect trait‐based adaptive strategies. However, little is known about how these networks ...change across spatial scales, and what drivers and mechanisms mediate this change.
This study bridges that gap by integrating functional traits related to plant carbon gain and water economy into the coordination network of Siberian elm (Ulmus pumila), a eurybiont that survives along a 3800 km environmental gradient from humid forest to arid desert.
Our results demonstrated that both stomatal density and stomatal size reached a physiological threshold at which adjustments in these traits were not sufficient to cope with the increased environmental stress. Network analysis further revealed that the mechanism for overcoming this threshold, the stomatal opening ratio, gratio, was represented by the highest values for centrality across different spatial scales, and therefore mediated the changes in the trait coordination network along environmental gradients. The mediating roles manifested as creating the highest maximum theoretical stomatal conductance (gsmax) but lowest possible gratio for pathogen defense in humid regions, while maintaining the gratio ‘sweet spot’ (c. 20% in this region) for highest water use efficiency in semihumid regions, and having the lowest gsmax and highest gratio for gas exchange and leaf cooling in arid regions.
These results suggested that the stomatal traits related to control of stomatal movement play fundamental roles in balancing gas exchange, leaf cooling, embolism resistance and pathogen defense. These insights will allow more accurate model parameterization for different regions, and therefore better predictions of species’ responses to global change.
Previous studies have shown that controlled deterioration treatment (CDT) induces programmed cell death in elm (Ulmus pumila L.) seeds, which undergo certain fundamental processes that are comparable ...to apoptosis in animals. In this study, the essential characteristics of mitochondrial physiology in elm seeds during CDT were identified by cellular ultrastructural analysis, whole‐body optical imaging, Western blotting and semi‐quantitative RT–PCR. The alteration in mitochondrial morphology was an early event during CDT, as indicated by progressive dynamic mitochondrial changes and rupture of the mitochondrial outer membrane; loss of mitochondrial transmembrane potential (Δψₘ) ensued, and mitochondrial ATP levels decreased. The mitochondrial permeability transition pore inhibitor cyclosporine A effectively suppressed these changes during ageing. The in situ localization of production of reactive oxygen species (ROS), and evaluation of the expression of voltage‐dependent anion‐selective channel and cyclophilin D indicated that the levels of mitochondrial permeability transition pore components were positively correlated with ROS production, leading to an imbalance of the cellular redox potential and ultimately to programmed cell death. Pre‐incubation with ascorbic acid slowed loss of mitochondrial Δψₘ, and decreased the effect of CDT on seed viability. However, there were no significant changes in multiple antioxidant elements or chaperones in the mitochondria during early stages of ageing. Our results indicate that CDT induces dynamic changes in mitochondrial physiology via increased ROS production, ultimately resulting in an irreversible loss of seed viability.
We investigated the effects of seed burial depth and soil water content on seedling emergence and growth of Ulmus pumila var. sabulosa (sandy elm), an important native tree species distributed over ...the European-Asian steppe. Experimental sand burial depths in the soil were 0.5, 1.0, 1.5, 2.0 and 2.5 cm, and soil water contents were 4%, 8%, 12% and 16% of field capacity. All two-way ANOVA (five sand burial depths and four soil water contents) results showed that seed burial depths, soil water content and their interactions significantly affected all the studied plant variables. Most of the times, seedling emergence conditions were greater at the lower sand burial depths (less than 1.0 cm) than at the higher (more than 1.0 cm) seed burial depths, and at the lower water content (less than 12%) than at the higher soil water content. However, high seed burial depths (more than 1.5 cm) or low soil water content (less than 12%) reduced seedling growth or change in the root/shoot biomass ratios. In conclusion, the most suitable range of sand burial was from 0.5 to 1.0 cm soil depth and soil water content was about 12%, respectively, for the processes of seedling emergence and growth. These findings indicate that seeds of the sandy elm should be kept at rather shallow soil depths, and water should be added up to 12% of soil capacity when conducting elm planting and management. Our findings could help to create a more appropriate sandy elm cultivation and understand sparse elm woodland recruitment failures in arid and semi-arid regions.
During seed maturation, the seed deposits storage compounds (starches, oils, and proteins), synthesizes defense compounds, produces a seed coat, initiates embryo dormancy, and becomes desiccated. ...During the late-maturation stage, seed storage compound contents and compositions change dramatically. Although maturation has been extensively studied in model species and crops, it remains less well characterized in woody perennial plants. In this study, we conducted morphological and cytological observations, transcriptome profiling, and chemical constituent analysis of elm (Ulmus pumila L.) seeds during the late-maturation stage. Light and electron microscopy revealed that closely packed yet discrete lipid bodies frequently surrounded the densely stained protein bodies, and the protein bodies became irregular or even partially disintegrated at the end of seed development. RNA-seq detected substantial transcriptome changes during the late-maturation stage, and pathway enrichment analysis showed that the differentially expressed genes were associated with phenylpropanoid biosynthesis, starch and sucrose metabolism, plant–pathogen interactions, and hormone signal transduction. Furthermore, we used mass spectrometry imaging to detect the relative intensity and spatial distribution of fatty acids, phospholipids, and waxes in elm seeds. Our findings provide a framework for understanding the changes in cytological features and chemical composition during the final stage of elm seed development, and a detailed reference for seed development in woody plants.
Ulmus pumila tree-dominated temperate savanna, which is distributed widely throughout the forest-steppe ecotone on the Mongolian Plateau, is a relatively stable woody-herbaceous complex ecosystem in ...northern China. Relatively more attention has been paid to the degradation of typical steppe areas, whereas less focus has been placed on the succession of this typical temperate savanna under the present management regime. In this study, we established 3 sample plots 100 m100 m in size along a gradient of fixed distances from one herder's stationary site and then surveyed all the woody plants in these plots. A spatial point pattern analysis was employed to clarify the spatial distribution and interaction of these woody plants. The results indicated that old U. pumila trees (DBH greater than or equal to 20 cm) showed a random distribution and that medium U. pumila trees (5 cm less than or equal to DBH < 20 cm) showed an aggregated distribution at a smaller scale and a random distribution at a larger scale; few or no juvenile trees (DBH < 5 cm) were present, and seedlings (without DBH) formed aggregations in all 3 plots. These findings can be explained by an alternate seasonal grazing-mowing regime (exclosure in summer, mowing in autumn and grazing in winter and spring); the shrubs in all 3 plots exist along a grazing gradient that harbors xerophytic and mesophytic shrubs. Of these shrubs, xerophytic shrubs show significant aggregation at a smaller scale (0-5.5 m), whereas mesophytic shrubs show significant aggregation at a larger scale (0-25 m), which may be the result of the dual effects of grazing pressure and climate change. Medium trees and seedlings significantly facilitate the distributions of xerophytic shrubs and compete significantly with mesophytic shrubs due to differences in water use strategies. We conclude that the implementation of an alternative grazing-mowing regime results in xerophytic shrub encroachment or existence, breaking the chain of normal succession in a U. pumila tree community in this typical temperate savanna ecosystem. This might eventually result in the degradation of the original tree-dominated savanna to a xerophytic shrub-dominated savanna.
•Chlorophyll and carotenoids content changed with seasons in U. pumila leaves.•Flavonoids gradually accumulated with seasonal changes in U. pumila leaves.•UpCrtR-b could significantly increase ...carotenoid accumulation.
Ulmus pumila ‘Zhonghua Jinye’ is an important landscape tree species because of its golden leaves. Leaf coloration is the main factor that determines the ornamental and economic value of U. pumila. Gene expression and metabolite accumulation patterns were studied by transcriptome and metabolome to explore the physiological and molecular mechanisms of leaf color changes in U. pumila. The results showed that the leaf color change of U. pumila was regulated by the metabolism of chlorophyll, flavonoids, and carotenoids. The content of total chlorophyll and chlorophyll a decreased gradually with seasonal changes, which was mainly caused by the obstruction of chlorophyll synthesis and the activation of the chlorophyll degradation pathway. Among them, the expression level of chlorophyll synthesis-related genes (GluTR, UROD, PPO, and POR) were down-regulated, while certain genes (CHLG, CAO, HCAR, PPH, and PAO) in the chlorophyll degradation pathway were significantly up-regulated. In addition, flavonoids gradually accumulated with seasonal changes. Among them, twenty-six key genes (PAL, 4CL, CHS, F3H, FLS, 3GT, DFR, and ANS) in flavonoid biosynthesis were involved in regulation of flavonol and anthocyanin biosynthesis. Furthermore, carotenoids (lutein, zeaxanthin, and β-carotene) were also mainly accumulated in July and August. Finally, the candidate gene, UpCrtR-b, in carotenoid biosynthesis was identified in the present study and was found to be expressed in plastids by functional verification. In tobacco, overexpression of UpCrtR-b could increase carotenoid accumulation and make tobacco leaves yellowish. This study revealed the molecular mechanism of leaf color regulation in U. pumila, and provided a theoretical basis for better utilization of this species as a landscape tree, which also provides the possibility for further enriching the variation mechanism and cultivating colored leaf plants.
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L. is an excellent afforestation and biofuel tree that produces high-quality wood, rich in starch. In addition,
is highly adaptable to adverse environmental conditions, which is conducive to its ...utilization for vegetating saline soils. However, little is known about the physiological responses and transcriptional regulatory network of
under salt stress. In this study, we exposed five main cultivars in saline-alkali land (Upu2, 5, 8, 11, and 12) to NaCl stress. Of the five cultivars assessed, Upu11 exhibited the highest salt resistance. Growth and biomass accumulation in Upu11 were promoted under low salt concentrations (<150 mM). However, after 3 months of continuous treatment with 150 mM NaCl, growth was inhibited, and photosynthesis declined. A transcriptome analysis conducted after 3 months of treatment detected 7009 differentially expressed unigenes (DEGs). The gene annotation indicated that these DEGs were mainly related to photosynthesis and carbon metabolism. Furthermore, PHOTOSYNTHETIC ELECTRON TRANSFERH (UpPETH), an important electron transporter in the photosynthetic electron transport chain, and UpWAXY, a key gene controlling amylose synthesis in the starch synthesis pathway, were identified as hub genes in the gene coexpression network. We identified 25 and 62 unigenes that may interact with PETH and WAXY, respectively. Overexpression of UpPETH and UpWAXY significantly increased the survival rates, net photosynthetic rates, biomass, and starch content of transgenic
plants under salt stress. Our findings clarify the physiological and transcriptional regulators that promote or inhibit growth under environmental stress. The identification of salt-responsive hub genes directly responsible for photosynthesis and starch synthesis or metabolism will provide targets for future genetic improvements.
NO can modulate carbohydrate metabolism at the post-translational level and activate glutathione and methionine metabolism at the transcriptional level, alleviating cell death in elm seeds during ...ageing.
Abstract
Seed ageing is a major problem in the conservation of germplasm resources. The involvement of possible signalling molecules during seed deterioration needs to be identified. In this study, we confirmed that nitric oxide (NO), a key signalling molecule in plants, plays a positive role in the resistance of elm seeds to deterioration. To explore which metabolic pathways were affected by NO, an untargeted metabolomic analysis was conducted, and 163 metabolites could respond to both NO and the ageing treatment. The primary altered pathways include glutathione, methionine, and carbohydrate metabolism. The genes involved in glutathione and methionine metabolism were up-regulated by NO at the transcriptional level. Using a biotin switch method, proteins with an NO-dependent post-translational modification were screened during seed deterioration, and 82 putative S-nitrosylated proteins were identified. Eleven of these proteins were involved in carbohydrate metabolism, and the activities of the three enzymes were regulated by NO. In combination, the results of the metabolomic and S-nitrosoproteomic studies demonstrated that NO could activate glycolysis and inhibit the pentose phosphate pathway. In summary, the combination of these results demonstrated that NO could modulate carbohydrate metabolism at the post-translational level and regulate glutathione and methionine metabolism at the transcriptional level. It provides initial insights into the regulatory mechanisms of NO in seed deterioration.
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